1. Field of Invention
The invention is related to methods and apparatus for securely locking a test device in place while load related measurements are taken.
2. Description of Related Art
Currently, a radial stiffness contact analyzer (RASCAL) machine can be used to measure performance qualities of a test tire, such as vertical, lateral and fore/aft stiffness. Generally, these tests can be accomplished by either pressing the test tire against a stationary load plate for vertical stiffness measurements, pressing the tire against a movable load plate for lateral and fore/aft stiffness measurement, or holding the test tire stationary while applying a force to a contact surface of the tire via a load plate. As a result of knowing the load or force exerted on the test tire and measuring the resulting deformation of the test tire, a stiffness of the test tire can be determined.
For example, in order to measure fore/aft stiffness of a test tire, the test tire can be mounted on a tire spindle of the radial stiffness contact analyzer. The tire spindle supporting the test tire is then locked in place by a locking assembly so that it will not rotate. Next, a contact surface of the test tire is then brought into contact with a load plate at a predetermined force. The force with which the test tire is brought into contact with the load plate is sufficient to prevent slippage between the test tire and load plate. A force is subsequently applied to the load plate, for example by a hydraulic cylinder or the like, in order to urge the load plate to move under the tire. The force applied to the load plate in turn results in a force being applied to the test tire. The force applied to the test tire also applies a torque or moment about the tire spindle. While the force is being applied, a load cell, linear transducer, or the like, can measure the corresponding deformation of the test tire. Based on these measurements, a stiffness of the test tire can be determined.
Presently, the locking assembly used to lock the tire spindle into place, and thereby to prevent rotation of the tire spindle and test tire, is a pin and sleeve assembly. In such an assembly, the pin is mounted on a stationary housing of the radial stiffness contact analyzer and is used to engage the sleeve mounted on the rotating tire spindle. In other words, the pin is extended to seat within the sleeve, and therefore the tire spindle is no longer able to rotate. Once held in place, the radial stiffness contact analyzer can perform stiffness measurements.
However, a problem with the above-described locking assembly is that the simple pin does not securely engaged the sleeve on the tire spindle, and therefore the tire spindle is able to slightly rotate until the clearances between the pin and sleeve are taken up. This is due in part to the inherent design of the pin and sleeve assembly which require some amount of space or tolerance between the pin and sleeve in order for the pin to be able to move in and out of the sleeve. As a result, there is a problem that the test tire is free to rotate until the clearances are taken in the locking assembly, which often results in inaccurate stiffness measurements of the test tire.